Method of managing radio resources in a cellular radio system

ABSTRACT

In a method and a system for managing resources within a cellular radio system servicing a geographical area, the serviced area is divided into at least two types and additional radio resources is provided to mobile stations located within one of the areas being deemed to be more sensitive for interference compared to mobile stations located within the other area.

TECHNICAL FIELD

The present invention relates to a method and a system for managingradio resources in a cellular radio system.

BACKGROUND

RRM (Radio Resource Management) is commonly utilized to handle theallowable radio resources in mobile communication, especially from thethird generation systems. Radio Resource management includes managementof many different resources within a cellular radio system including RA(Random Access). AC (Admission Control), CA (Code Allocation), HO (HandOver), PC (Power Control), LC (Load Control)/CC (Congestion Control),and so on.

TD-SCDMA (Time Division-Synchronization Code Division Multiple Access)is one of the third generation mobile communication standards. Someadvanced radio and processing technologies such as TDD (Time DivisionDuplex) mode, Uplink Synchronization, Smart Antennas, Joint Detection.Dynamic Channel Allocation are used in TD-SCDMA. Some of the advancedradio technologies used for TD-SCDMA makes radio resource managementmore challenging than in other third generation radio systems.

In TD-SCDMA, there is no soft handover like for example in WCDMA(Wideband Code Division Multiple Access). In TD-SCDMA, hard handover issupported: although some networks can support Baton hand over fordedicate channels in TD-SCDMA. Due to the lack of soft-handover inTD-SCDMA networks, users located close to a cell border will sometimessuffer from a bad QoS (quality of service). In some circumstances theQoS cannot be kept within specified limits and a user close to a cellborder can not be served rightly and timely.

Hence, there exist a need for a method and a system that is able toimprove the QoS in cellular radio systems such as TD-SCDMA. In suchsystems, there are lots of challenges to perform cell selection, randomaccess, admission control, radio resource allocation and so forth

SUMMARY

It is an object of the present invention to overcome or at least reducesome of the problems as outlined above.

It is another object of the present invention to provide a method and asystem that is capable of providing an improved Quality of Service (QoS)for users in a cellular radio system.

It is yet another object of the present invention to provide a methodand system that is capable of providing an acceptable Quality of Servicefor all mobile stations located within an area serviced by a cellularradio system.

These objects and others are obtained by the method and system as setout in the appended claims. Thus, in accordance with the invention, amultitude of cells of a cellular radio system are grouped together andavailable radio resource for all of the cells of the group is managed asa whole.

Also, in accordance with the present invention, a first area, where theinter-cell interference is a challenge for QoS guarantee is formedwithin an area covered by a group of cells. The remaining area of thegroup of cells will constitute a normal, second, area. Users located inthe first area can be termed sensitive users and users in the secondarea can be termed normal users.

In accordance with one embodiment the Radio Resource Algorithm appliedwithin the area formed by a group of cells is configured to giveadditional resources to sensitive users compared to normal users. Inparticular the Radio Resource Algorithm can be configured to optimizethe number of users within the group that is given a Quality of Servicethat is at least equal to the minimum required Quality of Service foreach user.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way ofnon-limiting examples and with reference to the accompanying drawings,in which:

FIG. 1 is a view of a cellular radio system.

FIG. 2 is a view of a cellular radio system with sector configuration,

FIG. 3 is a view of a cellular radio system divided into different typesof areas,

FIG. 4 is a view of a cellular radio system with a mobile stationlocated close to the border of two cells.

FIG. 5 is a view of radio network controller RNC used to manage radioresources within cells controlled by the RNC, and

FIG. 6 is a flowchart illustrating steps performed when managing radioresources in a radio system using different radio resource allocationalgorithms for different users.

DETAILED DESCRIPTION

Typically, the primary challenge of RRM algorithms is to guarantee theQoS of users close to a cell border. This is because those usersexperience a radio link with a large path-loss towards the serving radiobase station, Node-B, as well as they experience severe inter-cellinterference. This especially for those users located in the overlappedarea (two or more adjacent cells cover the area with similar path-losstowards the serving radio base stations) as shown as in FIG. 1. In fact,there are also small overlapped areas between sectors. i.e. the areaclose to the boundary of sectors.

For CDMA, with the property of self-interference, adjacent cells can bebundled into a group with common air interface resources wherein theradio resource allocation and management is performed in order to get agroup-optimized balance of resource utilization among all of the cellsof such a group of cells.

For instance, in accordance with one embodiment of the present inventionunder common sector configuration with 120° coverage, every threeneighbour cells can be viewed as a resource-handling group covering acommon area as the striped joint cell-area indicates in FIG. 2.

In FIG. 2, three radio base station sites are shown at 201, 203 and 205respectively. The radio base stations 201, 203 and 205 are all connectedto a radio network controller RNC 207. In a radio base station siteconfiguration as the one shown in FIG. 2, the three cells served by thethree radio base stations 201, 203 and 205 will suffer from interferencesignals generated by each other in the striped area. It is in generaldifficult to handle this type of interference at the air-interface inmobile network due to the complicated radio propagation characteristics.Therefore, these three cells are treated as a group for radio resourcemanagement in accordance with the present invention.

In order to obtain an improved Quality of Service within the cellsdepicted in FIG. 2, the coverage for a cell can be classified intodifferent part, e.g. a sensitive area and a normal area. For TD-SCDMA,the sensitive area can be defined as the region close to the border ofother cells due to a radio link with a large path-loss towards theserving Node-B and the severe inter-cell interference. Because there isno soft handover in TD-SCDMA. QoS for the users in the sensitive areamay not be guaranteed in TD-SCDMA. Also, sometimes it is challenging todecode the broadcasted cell information and challenging to pass therandom access procedure for these users to such degree that failures maybe experienced. The remaining part of the cell is defined as the normalarea, where these users has a good enough radio link with servingNode-Bs and their QoS is easily guaranteed by simple state of the artRRM algorithms.

Hence, in an exemplary cellular radio system such as a TD-SCDMA radiosystem the sensitive area can be defined to correspond to the stripedarea in FIG. 3, i.e. areas being located some predetermined distancefrom the nearest radio base station, and the remaining area covered bysuch a radio system is defined to correspond to the non-striped area.

Different users within the coverage area of a radio system are thenclassified based on where in the coverage area of the radio system auser is located. Hence, users within the sensitive area can beclassified as sensitive users whereas users within the remaining areacovered by the radio system can be classified as normal users.

The users belonging to the different groups can then be treateddifferently for example by applying different RRM algorithms ordifferent parameter setting. In particular, users in sensitive area canadvantageously by given a more generous allocation of radio resources.This can for example be achieved by assigning, higher service priorityto such users and/or applying adjusted thresholds reflecting therequirements in the specific situation for such users.

The principle of classifying an area serviced by a radio network intosensitive and normal area could be different based on the differentrequirement of network planning and optimization. For instance, thereceived broadcasted channel power level or the received dedicatechannel power level, the CINR (Carrier-Interference-Noise Ratio), theBLER (Block Error Ratio), or the physical distance between the user andserving base station/Node-B, etc can be used to classify the type ofareas within a joint coverage area served by a group of cells.

The Radio Resource Management functions applied in different scenariosmay differ: For example after a Radio Network Controller of a radiosystem has gained knowledge about the classification of a mobilestation, i.e. if the mobile station is regarded as normal or sensitive,the RNC may for example apply any of the following RRM algorithms.

When mobile station or User Equipment UE has a communication request, itwill send the request to the current serving base station, and thenexecute a random access procedure for an attempt to access the radionetwork. For TD-SCDMA, the cell selection is typically based on receivedDwPCH (Downlink Pilot Channel) power level which is transmitted in theDwPTS (Downlink Pilot Time Slot). In such a scenario it is possible thata user receives two or more approximately equivalent DwPCH signal powerlevels from different cells in the same group if the user has similardistance to these base stations. Further, in such a scenario where auser receives approximately equal DwPCH signal power levels from morethan one cell, the cell selection may result in that the selectedserving cell is not the best one.

As a result a random access attempt to a particular cell may fail. Inother words, the random access procedure has to deal with the challengesfrom users close to the border of two or more cells, i.e. the sensitiveusers.

To improve the likelihood of a successful random access procedure for asensitive user, a radio resource algorithm allowing more chances toaccess more adjacent cells can be provided. For example, assume thescenario depicted in FIG. 4, where a user/mobile station 401 is locatedapproximately equally close to the three base stations 201, 203 and 205respectively. If the user 401 first tries to access the cell serviced bythe base station 201 and fails, a subsequent attempt to access the radiosystem may be directed to another cell. In an exemplary embodiment, whenthe sensitive user 401 can not access a current cell by means of normalrandom access procedure with several sending preambles of SYNC_UL, i.e.one signal used in the Random access procedure of TD-SCDMA, but nofeedback is received from the base station on the Fast Physical PhysicalAccess Channel (FPACH), as well one signal used in RA procedure ofTD-SCDMA, the user/mobile station 401 can be adapted to try to make another access attempt to an other adjacent cells in the group of cells insome predetermined order.

In theory, the access success rate of a random access procedure isguaranteed by many things such as maximum transmission power ofterminals, initial transmission power setting by open-loop powercontrol, access attempt times and so on. But under any networkdeployment, there are random access failures due to the radio linkvariability when moving and similar events. This likelihood of a randomaccess failure for a random access procedure is increased for theaforementioned sensitive users. Therefore, such users can be assignedadditional radio resources in accordance with the above schematicdescription or for some other procedure giving priority to a sensitiveuser.

After a random access procedure, Admission Control (AC) and DynamicChannel Allocation (DCA) will be triggered to decide to admit the useror not and assign the suitable radio resource units for bearer in forexample TD-SCDMA. These two functions are important in

RRM in order to control system robustness and radio resource utilizationrate. For TD-SCDMA, there is a close relationship between admissioncontrol and channel allocation due to its timeslot-based bearercharacteristics.

In accordance with one embodiment of the present the invention, amulti-cell group based radio resource allocation scheme can beimplemented by first applying a straight forward traditional algorithmlike random allocation or similar conventional schemes and then to usean additional re-allocation scheme for one or more particular users,especially for sensitive users.

Typically, a particular user can be identified by reduction/changes inthe measurement report of received power level on dedicate channels. There-allocation algorithm can for example be build as a virtualpriority-based resource allocation guard layer overlapped on the normallayer to guarantee the QoS of sensitive users. For example, a resourcepriority based algorithm can be used to deal with a user experience avery bad radio link and its QoS is lower than the minimum requirementfor at least some predetermined period of time or if there is a risk ofdropping the user.

For TD-SCDMA, the allowable radio resource units include carrier, timeslot, channelisation codes. Spatial degree is additive handling resourceif SDMA is used. If a User/mobile station, such as the mobile station401 in FIG. 4 satisfies any condition triggering a re-allocation ofradio resources, the network will re-allocate it to a pre-designatedfrequency or/and slot to guarantee its QoS. Because the primaryinterference in TD-SCDMA is inter-cell interference, different radioresource priority setting among the cells in a group can isolateeffectively and minimize the inter-cell interference in the sensitivearea.

For example, when the user/mobile station 401 satisfies any conditiontriggering re-allocation, the network will check its current assignedresource from every domain. Next, the network will try to re-allocatethe highest priority resource units of its serving cells. In the abovecase, if the current slot is 3 but 1 is the highest priority slot, thesystem will attempt to transfer it to time slot 1. Given the user isalready in slot 1: the system will try to transfer it to the carrierwith the highest priority. If there is no resource with higher priority,the terminal may have to be dropped.

Based on the above resource priority setting scheme, the admissioncontrol and handover functions could be taken into account as a whole.That is, the admission control can be set to first estimate theadmission effect for users with normal resource units and for users withprior/pre allocated resource units, and then set different weights tothese two type of estimation results to decide to admit or not. Theprior/pre allocation is a default allocation of all cell/cell groupresources division to avoid or minimize inter-cell interference in a lowload situation. Also, handover measurement can be made to pay additionalattention to sensitive users, and the system can allocate the prior/preallocated units to the handover users due to most handovers aretriggered by bad QoS.

Moreover, Load Control LC and Congestion Control CC functions can be setto treat different users' individually. For example, the aforementionedre-allocation algorithm can be seen as a load control scheme for speechusers depending on the definition of the relationship of overload andthe triggering event for a re-allocation.

Typically, a down switch method, i.e. lower allocation of allowedbitrate, is used to avoid network congestion for packet switched PStraffic. In a preferred embodiment of the present invention, the networkpays special attention to monitor the packet switched users in asensitive area than users in a normal area. This may for example resultin that either the sensitive user and/or the normal users are servicedown switched to support the prioritized sensitive users' services.

In FIG. 5 a view of an RNC 207 implementing a radio resource managementalgorithm in accordance with the above is shown. The RNC 207 maycomprise a control unit 501 for managing the radio resources within thecells under control of the RNC. In addition the RNC may comprise amemory 503 for storing suitable software, in particular a computerprogram product that when executed by the RNC will cause the RNC tocontrol the radio resources within the cells under control of the RNC inaccordance with the program segments of the software of the programproduct.

In FIG. 6 a flowchart illustrating exemplary steps performed by the RNC207 when applying a radio resource management algorithm in accordancewith a preferred embodiment of the invention. First, in a step 601, thenetwork divides a group of cells under control of the RNC 207 into atleast two different area types. A first area where users of the radionetwork potentially will experience difficulties in maintaining aQuality of Service and a second area constituting the remaining area ofthe group of cells. Of course the area may be divided into more than twotypes if that should be advantageous in some scenario.

Next, in a step 603, all users within the first area will be servicedusing a different radio resource algorithm than the users in the secondarea. In particular such a different radio resource algorithm may be anyof algorithms as set out above.

Using the method and system as described herein will provide a betterQuality of Service for users in a cellular radio system. In particularusers located in areas normally suffering from a bad quality of servicecan be provided with an improved Quality of Service. In addition therisk of dropping connections will be reduced.

1. A method of managing resources within a cellular radio systemservicing a geographical area, the method comprising: dividing theserviced geographical area into at least two types, the at least twotypes including a first area where Quality of Service is deemed to bedifficult to maintain based on some predefined condition, and a secondarea outside the first area, and providing additional radio resources tomobile stations located within the first area compared to mobilestations located within the second area.
 2. The method according toclaim 1, where the geographical area served by the cellular radio systemis divided into groups of cells associated with Radio Base Stationsbeing controlled by a same Radio Network Controller (RNC), and where theradio resources of each group is managed as one radio resource handlinggroup.
 3. The method according to claim 2, where the cellular radiosystem is configured with a common sector configuration with about 120°coverage, and where every three neighbour cells is grouped as one radioresource-handling group.
 4. The method according to claim 1, where thefirst area is defined as a region close to a border of radio cellshandled by other radio base stations.
 5. The method according to claim1, where a different radio resource management (RRM) algorithm or adifferent parameter setting are applied for mobile stations located inthe first area.
 6. The method according to claim 5, where a higherservice priority and/or reduced target thresholds are applied to mobilestations located in the first area.
 7. The method according to claim 1,where a radio resource algorithm allowing additional opportunities toaccess at least one adjacent cell if a random access attempt to acurrent serving cell fails is provided for mobile stations located inthe first area.
 8. The method according to claim 1, where a differentreallocation algorithm is applied to some mobile stations based on ameasurement report of at least one dedicated channel.
 9. The methodaccording to claim 1, where a resource priority based algorithm isapplied to a mobile station if the Quality of Service (QoS) is lowerthan a predetermined threshold value for at least a predetermined periodof time or if there is a significant probability of dropping aconnection to the mobile station.
 10. A node for managing resourceswithin a cellular radio system servicing a geographical area, the nodecomprising: means for dividing the serviced geographical area into atleast two types, the at least two types including a first area whereQuality of Service is deemed to be difficult to maintain based on somepredefined condition, and a second area outside the first area, andmeans for providing additional radio resources to mobile stationslocated within the first area compared to mobile stations located withinthe second area.
 11. The node according to claim 10, where the means fordividing includes: means for dividing the geographical area served bythe cellular radio system into groups of cells associated with RadioBase Stations being controlled by a same Radio Network Controller (RNC),and where the radio resources of each group is managed as one radioresource handling group.
 12. The node according to claim 11, furthercomprising: means for grouping every three neighbour cells, of thecellular radio system configured with a common sector configuration withabout 120° coverage, as one radio resource-handling group.
 13. The nodeaccording to claim 10, further comprising: means for setting the firstarea as a region close to a border of radio cells handled by other radiobase stations.
 14. The node according to claim 10, further comprising:means for applying a different radio resource management (RRM) algorithmor different parameter setting for mobile stations located in the firstarea.
 15. The node according to claim 14, further comprising: means forgiving a higher service priority and/or applying reduced targetthresholds to mobile stations located in the first area.
 16. The nodeaccording to claim 10, further comprising: means for allowing additionalopportunities to access at least one adjacent cell if a random accessattempt to a current serving cell fails is provided for mobile stationslocated in the first area.
 17. The node according to claim 10, furthercomprising: means for applying a different re-allocation algorithm tosome mobile stations based on a measurement report of at least onededicated channel.
 18. The node according to claim 10, furthercomprising: means for applying a resource priority based algorithm to amobile station if the Quality of Service (QoS) is lower than apredetermined threshold value for at least a predetermined period oftime or if there is a significant probability of dropping a connectionto the mobile station.
 19. A computer program product that comprisesprogram segments that, when executed on a computer, causes the computerto perform a method comprising: dividing the serviced geographical areainto at least two types, the at least two types including a first areawhere Quality of Service is deemed to be difficult to maintain based onsome predefined condition, and a second area outside the first area; andproviding additional radio resources to mobile stations located withinthe first area compared to mobile stations located within the secondarea.
 20. The computer program product of claim 19, where thegeographical area served by the cellular radio system is divided intogroups of cells associated with Radio Base Stations being controlled bya same Radio Network Controller (RNC), and where the radio resources ofeach group is managed as one radio resource handling group.